1. Field of the Invention
The present invention relates generally to a method of forming interconnection patterns and, more particularly, to an improved method of forming interconnection patterns, which enables prevention of corrosion of metal interconnections. The invention further relates to an apparatus for manufacturing such a semiconductor device. The invention also relates to a semiconductor device having such interconnection patterns.
2. Description of the Background Art
In a manufacture process of a semiconductor device, the step of forming interconnection patterns is indispensable. FIGS. 4A and 4B show cross-sectional views showing the step of forming interconnection patterns.
With reference to FIG. 4A, a gate 31 and an interlayer insulation film 32 are formed on a semiconductor substrate 30. A contact hole 33b for exposing source/drain regions (not shown) of a transistor and a contact hole 33a for exposing a portion of a surface of gate 31 are formed in interlayer insulation film 32. An interconnection layer 34 made of an aluminum alloy film is then formed on interlayer insulation film 32 so as to fill these contact holes 33a and 33b. A resist 35 patterned in a predetermined form is formed on interconnection layer 34.
Referring to FIG. 4B, interconnection patterns 36 are formed by selectively etching interconnection layer 34, with resist 35 used as mask.
As a conventional method of forming interconnection patterns of aluminum alloy, such a method is provided that aluminum interconnection layer 34 is subjected to a wet etching process employing a mixed solution of phosphoric acid, nitric acid, etc., using resist 35. This method, however, has difficulties in formation of micro patterns less than or equal to 3 .mu.m due to an enhancement of etching extending under resist patterns 35, a so-called under-etching. Thus, a method employing a reactive ion etching (hereinafter referred to as RIE etching) using a gas such as of chlorine or a compound containing chlorine, e.g., Cl.sub.2, SiCl.sub.4, BCl.sub.3, etc. has been adopted for formation of such micro patterns.
A description will be given in detail on the conventional method of forming interconnection patterns by RIE etching and also on disadvantages of the conventional method.
A lower insulator film 3 is formed on a semiconductor substrate 30, with reference to FIG. 5A. A metal interconnection layer 2 such as of AlSi, AlSiCu, Cu, Mg, etc. is then formed on lower insulator film 3. A resist pattern 1 of a predetermined form is then formed on metal interconnection layer 2.
Referring to FIG. 5B, metal interconnection layer 2 is subjected to reactive ion etching by employing a halogen-type gas containing chlorine such as Cl.sub.2, SiCl.sub.4, BCl.sub.3 and so on, with resist pattern 1 used as mask. This reactive ion etching causes metal interconnection layer 2 to be selectively etched, resulting in formation of an interconnection pattern 2a. At this time, a protection film 4 including halogen is formed on sidewalls of resist pattern 1 and interconnection pattern 2a. Protection film 4 serves to suppress isotropical etching and enhance anisotropy. This protection film is made by a complicated reaction of components of the resist, interconnection layer and halogen-type gas and includes halogen.
An ashing processing with a O.sub.2 gas 5 is carried out to remove resist pattern 1, with reference to FIGS. 5B and 5C. Even after the ashing processing, a protection film 6 containing halogen remains on the sidewall of interconnection pattern 2a. The micro interconnection pattern 2a is thus formed.
This method, however, has a disadvantage that when the semiconductor device is taken out in the atmosphere, a corroded portion 9 is formed on the sidewall of interconnection pattern 2a, as shown in FIG. 5D, thereby inducing disconnection of interconnection pattern 2a.
The causes for the corrosion are as follows: protection film 6 contains halogen, e.g., chlorine, and when exposed in the atmosphere, reacts with water molecules 7 in the atmosphere to generate a hydrochloric acid. The generated hydrochloric acid acts on interconnection pattern 2a, to produce reaction products 8 (e.g., metal chloride). When reaction products 8 are separated from the sidewall of interconnection pattern 2a, interconnection pattern 2a becomes gradually corroded.